Semiconductor optical amplifiers (SOAs) have been widely used as in-line amplifiers in fiber-optic communication systems to boost the optical signal directly without requiring conversion to the electrical domain, saving the cost of regenerators and system complexity. The SOA functions like a laser without a feedback mechanism or cavity provided, and is called a traveling-wave amplifier. It is based on a two-terminal diode (p-i-n) structure to provide optical gain via current injection. SOAs can be integrated with other photonic components, such as lasers or modulators, for optical signal amplification or optical gating purposes and form a photonic integrated circuit (PIC).
A part of the background hereof lies in the development of heterojunction bipolar transistors which operate as light-emitting transistors and transistor lasers. Reference can be made for example, to U.S. Pat. Nos. 7,091,082, 7,286,583, 7,354,780, 7,535,034, 7,693,195, 7,711,015, 7,813,396, 7,888,119, 7,888,625, and 7, 953,133; U.S. Patent Application Publication Numbers US2005/0040432, US2005/0054172, US2008/0240173, US2009/0134939, US 2010/0315018, and US2010/0103971; and to PCT International Patent Publication Numbers WO/2005/020287 and WO/2006/093883. Reference can also be made to the following publications: Light-Emitting Transistor: Light Emission From InGaP/GaAs Heterojunction Bipolar Transistors, M. Feng, N. Holonyak, Jr., and W. Hafez, Appl. Phys. Lett. 84, 151 (2004); Quantum-Well-Base Heterojunction Bipolar Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., and R. Chan, Appl. Phys. Lett. 84, 1952 (2004); Type-II GaAsSb/InP Heterojunction Bipolar Light-Emitting Transistor, M. Feng, N. Holonyak, Jr., B. Chu-Kung, G. Walter, and R. Chan, Appl. Phys. Lett. 84, 4792 (2004); Laser Operation Of A Heterojunction Bipolar Light-Emitting Transistor, G. Walter, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 85, 4768 (2004); Microwave Operation And Modulation Of A Transistor Laser, R. Chan, M. Feng, N. Holonyak, Jr., and G. Walter, Appl. Phys. Lett. 86, 131114 (2005); Room Temperature Continuous Wave Operation Of A Heterojunction Bipolar Transistor Laser, M. Feng, N. Holonyak, Jr., G. Walter, and R. Chan, Appl. Phys. Lett. 87, 131103 (2005); Visible Spectrum Light-Emitting Transistors, F. Dixon, R. Chan, G. Walter, N. Holonyak, Jr., M. Feng, X. B. Zhang, J. H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 88, 012108 (2006); The Transistor Laser, N. Holonyak and M Feng, Spectrum, IEEE Volume 43, Issue 2, February 2006; Signal Mixing In A Multiple Input Transistor Laser Near Threshold, M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Appl. Phys. Lett. 88, 063509 (2006); Collector Current Map Of Gain And Stimulated Recombination On The Base Quantum Well Transitions Of A Transistor Laser, R. Chan, N. Holonyak, Jr., A. James, and G. Walter, Appl. Phys. Lett. 88, 14508 (2006); Collector Breakdown In The Heterojunction Bipolar Transistor Laser, G. Walter, A. James, N. Holonyak, Jr., M. Feng, and R. Chan, Appl. Phys. Lett. 88, 232105 (2006); High-Speed (/spl ges/1 GHz) Electrical And Optical Adding, Mixing, And Processing Of Square-Wave Signals With A Transistor Laser, M. Feng, N. Holonyak, Jr., R. Chan, A. James, and G. Walter, Photonics Technology Letters, IEEE Volume: 18 Issue: 11 (2006); Graded-Base InGaN/GaN Heterojunction Bipolar Light-Emitting Transistors, B. F. Chu-Kung et al., Appl. Phys. Lett. 89, 082108 (2006); Carrier Lifetime And Modulation Bandwidth Of A Quantum Well AlGaAs/InGaP/GaAs/InGaAs Transistor Laser, M. Feng, N. Holonyak, Jr., A. James, K. Cimino, G. Walter, and R. Chan, Appl. Phys. Lett. 89, 113504 (2006); Chirp In A Transistor Laser, Franz-Keldysh Reduction of The Linewidth Enhancement, G. Walter, A. James, N. Holonyak, Jr., and M. Feng, Appl. Phys. Lett. 90, 091109 (2007); Photon-Assisted Breakdown, Negative Resistance, And Switching In A Quantum-Well Transistor Laser, A. James, G. Walter, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 90, 152109 (2007); Franz-Keldysh Photon-Assisted Voltage-Operated Switching of a Transistor Laser, A. James, N. Holonyak, M. Feng, and G. Walter, Photonics Technology Letters, IEEE Volume: 19 Issue: 9 (2007); Experimental Determination Of The Effective Minority Carrier Lifetime In The Operation Of A Quantum-Well n-p-n Heterojunction Bipolar Light-Emitting Transistor Of Varying Base Quantum-Well Design And Doping; H. W. Then, M. Feng, N. Holonyak, Jr., and C. H. Wu, Appl. Phys. Lett. 91, 033505 (2007); Charge Control Analysis Of Transistor Laser Operation, M. Feng, N. Holonyak, Jr., H. W. Then, and G. Walter, Appl. Phys. Lett. 91, 053501 (2007); Optical Bandwidth Enhancement By Operation And Modulation Of The First Excited State Of A Transistor Laser, H. W. Then, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 91, 183505 (2007); Modulation Of High Current Gain (β>49) Light-Emitting InGaN/GaN Heterojunction Bipolar Transistors, B. F. Chu-Kung, C. H. Wu, G. Walter, M. Feng, N. Holonyak, Jr., T. Chung, J.-H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 91, 232114 (2007); Collector Characteristics And The Differential Optical Gain Of A Quantum-Well Transistor Laser, H. W. Then, G. Walter, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 91, 243508 (2007); Transistor Laser With Emission Wavelength at 1544 nm, F. Dixon, M. Feng, N. Holonyak, Jr., Yong Huang, X. B. Zhang, J. H. Ryou, and R. D. Dupuis, Appl. Phys. Lett. 93, 021111 (2008); Optical Bandwidth Enhancement Of Heterojunction Bipolar Transistor Laser Operation With An Auxiliary Base Signal, H. W. Then, G. Walter, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 93, 163504 (2008); Bandwidth Extension By Trade-Off Of Electrical And Optical Gain In A Transistor Laser, Three-Terminal control, H. W. Then, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 94, 013509 (2009); Tunnel Junction Transistor Laser, M. Feng, N. Holonyak, Jr., H. W. Then, C. H. Wu, and G. Walter, Appl. Phys. Lett 94, 041118 (2009); Electrical-Optical Signal Mixing And Multiplication (2→22 GHz) With A Tunnel Junction Transistor Laser, H. W. Then, C. H. Wu, G. Walter, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 94, 101114 (2009); Scaling Of Light Emitting Transistor For Multigigahertz Optical Bandwidth, C. H. Wu, G. Walter, H. W. Then, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett, 94, 171101 (2009); Device Performance Of Light Emitting Transistors With C-Doped And Zn-Doped Base Layers, Y. Huang, J.-H. Ryou, R. D. Dupuis, F. Dixon, N. Holonyak, M. Feng, Indium Phosphide & Related Materials, 2009; IPRM '09. IEEE International Conference On 10-14 May 2009; Tilted-Charge High Speed (7 GHz) Light Emitting Diode, G. Walter, C. H. Wu, H. W. Then, M. Feng, and N. Holonyak, Jr. Appl. Phys. Lett. 94, 231125 (2009); 4.3 GHz Optical Bandwidth Light Emitting Transistor, G. Walter, C. H. Wu, H. W. Then, M. Feng, and N. Holonyak, Jr., Appl. Phys. Lett. 94, 241101 (2009); Resonance-Free Frequency Response Of A Semiconductor Laser, M. Feng, H. W. Then, N. Holonyak, Jr., G. Walter, and A. James, Appl. Phys. Lett. 95, 033509 (2009); 4-GHz Modulation Bandwidth of Integrated 2×2 LED Array, Chao-Hsin Wu; G. Walter, Han Wui Then, M. Feng, N. Holonyak, Photonics Technology Letters, IEEE Volume: 21, Issue 24, Publication Year: 2009, Page(s): 1834-1836, Date of Publication: 9 Nov. 2009; Physics Of Base Charge Dynamics In The Three Port Transistor Laser, H. W. Then, M. Feng, and N. Holonyak Appl. Phys. Lett. 96, 113509 (2010); Microwave Circuit Model Of The Three-Port Transistor Laser, H. W. Then, M. Feng, and N. Holonyak, J. Appl. Phys. 107, 094509 (2010); Distributed Feedback Transistor Laser, F. Dixon, M. Feng, and N. Holonyak; Appl. Phys. Lett. 96, 241103 (2010); Stochastic Base Doping And Quantum-Well Enhancement Of Recombination In An n-p-n Light-Emitting Transistor Or Transistor Laser, H. W. Then, C. H. Wu, M. Feng, N. Holonyak, and G. Walter, Appl. Phys. Lett. 96, 263505 (2010); Design And Operation Of Distributed Feedback Transistor Lasers, F. Dixon, M. Feng, and N. Holonyak, J. Appl. Phys. 108, 093109 (2010); and Temperature Dependence Of A High-Performance Narrow-Stripe (1 μm) Single Quantum-Well Transistor Laser, M. Feng, N. Holonyak, and A. James, Appl. Phys. Lett. 98, 051107 (2011). The foregoing documents describe, inter alia, the structure and operation of light-emitting transistors (LETs) and transistor lasers (TLs), at least some of which being of types that can be employed in making or practicing embodiments of the invention.
It is among the objectives hereof to improve on existing semiconductor optical amplifiers (SOAs) by improving one or more of the operation, versatility, flexibility, ease of integration, and cost of such devices. It is among the further objectives hereof to provide improved opto-electronic devices and methods.